Advanced lung cancer (non-small cell lung cancer) with a mutation in the EGFR (epidermal growth factor receptor) gene, which have disease progression after treatment with an EGFR inhibitor (erlotinib or gefitinib), and have progression of disease also after treatment with chemotherapy will be recruited. The trial has only one arm, of afatinib daily treatment. Blood and exhaled breath samples will be collected for investigations aiming to identify factors that predict response to afatinib.